Project Summary Odorant receptor (OR) genes exhibit an unusual form of random monoallelic expression, commonly referred to as monogenic or singular expression. In the mouse, olfactory sensory neurons express one allele of one OR gene from a large repertoire of >1,000 genes scattered throughout the genome. Current models for OR choice involve epigenetic mechanisms orchestrated by a genome-wide network of distributed enhancers. The Trace Amine Associated Receptors (TAARs) constitute a small olfactory receptor gene family that is also subject to singular expression. However, the epigenetic properties of TAARs differ from ORs in a number of key ways, calling into question whether both share a common mechanism of singular expression. The goal of this proposal is to characterize the mechanisms of singular expression of TAAR genes. We have identified the local enhancers that govern TAAR gene expression and will exploit this knowledge to test hypotheses about how these regulator elements orchestrate choice. The Aims of the proposal are to 1) identify the sequence motifs that are required for enhancer function, 2) elucidate the specificity and spatial extent of enhancer function, and 3) characterize the three-dimensional interaction landscape of the TAAR gene cluster. These experiments exploit unique aspects of the TAAR cluster to test and extend current models of monoallelic expression?a phenomenon that plays a critical role in myriad biological processes including dosage compensation, cell-type specification, phenotypic variation and disease pathogenesis.